1. Field of the Invention
The present invention relates to a bearing device and a pin for the bearing device, and more particularly, relates to a bearing device of a crawler track or the like that is used for a travel device of a construction machine and a pin for the bearing device.
2. Description of the Related Art
Generally, a travel device of a construction machine is configured as a result that a crawler track is winded around an idler and a sprocket. Then, as shown in FIG. 13, a crawler track 53 is configured by a plurality of links 54 to be endlessly coupled with each other and a plurality of shoe plates (not illustrated) or the like to be attached to these links 54. In other words, in the crawler track 53, the opposed links 54 are coupled in a longitudinal direction through a pin 57 and bushes 58 and 59, respectively to form a pair of endless bodies 60, and the shoe plates are attached to these endless bodies 60.
In this case, end portions 61 and 62 of the adjacent links 54 are superposed with each other, unilateral bushes 58 are pressed into holes 61a of the end portions 61 at the inside of the opposed links 54, and the pin 57 is rotatably inserted in the bushes 58. On this occasion, the end portions of the pin 57 are pressed into holes 62a of the end portions 62 at the outside of the opposed links 54. In addition, between the end portions 61 at the inside of the opposed links 54, the other bush 59 is externally fit in the pin 57. Further, lubrication oil is supplied between the pin 57 and the bushes 58 and 59. In addition, seal devices 64 and 65 are disposed between the bushes 58 and 59, and between the bush 58 and the end portion 62 of the link 54, respectively.
Accordingly, when the sprocket is rotatably driven, the crawler track 53 that is configured as described above is driven while maintaining an oval form. On this occasion, a unidirectional tractional force acts on the crawler track 53, and furthermore, when the crawler track 53 is traveling around the idler and the sprocket, a bearing device configured by the pin 57 and the bush 58 or the like may rotate around the idler and the sprocket. As a result, the bush 58 and the pin 57 are relatively rocked, and as shown in FIG. 14, conventionally, a slidable range H is formed, in which the outer peripheral face of the pin 57 and the inner peripheral face of the bush 58 partially and slidably contact with each other. In other words, under the condition that a pin axial center O of the pin 57 is decentered against a bush axial center O1 of the bush 58 in a certain direction, and then, the slidable range H is formed.
In this slidable range H, a center angle A centering on the pin axial center O is within the range of 70 degrees to 90 degrees. In addition, in the case that a strong tractional force acts on the pin 57 and the bush 58, a rocking angle (α/2+α/2) of the pin 57 with respect to the bush 58 is about 30 degrees. Therefore, a no-lubrication portion C (a center angle C1), to which the lubrication oil is not supplied even when the pin 57 and the bush 58 are rocked, is formed.
Therefore, if the operation is continued under such a condition, burn-in may occur between the pin 57 and the bush 58 even with a relatively low load (tension), so that this involves a problem with durability.